Itaconate is a nonamino organic acid exhibiting antimicrobial effects. It has been recently identified in cells of macrophage lineage as a product of an enzyme encoded by immunoresponsive gene 1 ( Irg1 ), acting on the citric acid cycle intermediate cis‐aconitate. In mitochondria, itaconate can be converted by succinate‐coenzyme A (CoA) ligase to itaconyl‐CoA at the expense of ATP (or GTP), and is also a weak competitive inhibitor of complex II. Here, we investigated specific bioenergetic effects of increased itaconate production mediated by LPS‐induced stimulation of Irg1 in murine bone marrow‐derived macrophages (BMDM) and RAW‐264.7 cells. In rotenone‐treated macrophage cells, stimulation by LPS led to impairment in substrate‐level phosphorylation (SLP) of in situ mitochondria, deduced by a reversal in the directionality of the adenine nucleotide translocase operation. In RAW‐264.7 cells, the LPS‐induced impairment in SLP was reversed by short‐interfering RNA(siRNA)—but not scrambled siRNA—treatment directed against Irg1. LPS dose‐dependently inhibited oxygen consumption rates (61‐91%) and elevated glycolysis rates (>21%) in BMDM but not RAW‐264.7 cells, studied under various metabolic conditions. In isolated mouse liver mitochondria treated with rotenone, itaconate dose‐dependently (0.5‐2 mM) reversed the operation of adenine nucleotide translocase, implying impairment in SLP, an effect that was partially mimicked by malonate. However, malonate yielded greater ADP‐induced depolarizations (3‐19%) than itaconate. We postulate that itaconate abolishes SLP due to 1) a “CoA trap” in the form of itaconyl‐CoA that negatively affects the upstream supply of succinyl‐CoA from the α‐ketoglutarate dehydrogenase complex; 2) depletion of ATP (or GTP), which are required for the thioesterification by succinate‐CoA ligase; and 3) inhibition of complex II leading to a buildup of succinate which shifts succinate‐CoA ligase equilibrium toward ATP (or GTP) utilization. Our results support the notion that Irg1 ‐expressing cells of macrophage lineage lose the capacity of mitochondrial SLP for producing itaconate during mounting of an immune defense.—Németh, B., Doczi, J., Csete, D., Kacso, G., Ravasz, D., Adams, D., Kiss, G., Nagy, A. M., Horvath, G., Tretter, L., Mócsai, A., Csépányi‐Kömi, R., Iordanov, I., Adam‐Vizi, V., Chinopoulos, C. Abolition of mitochondrial substrate‐level phosphorylation by itaconic acid produced by LPS‐induced Irg1 expression in cells of murine macrophage lineage. FASEB J. 30, 286‐300 (2016). www.fasebj.org

TP53 mutation hits energy metabolism and increases glycolysis in breast cancer

The redox dye methylene blue (MB) is proven to have beneficial effects in various models of neurodegenerative diseases. Here we investigated the effects of MB (100 nM, 300 nM, and 1 μM) on key bioenergetic parameters and on H2O2 production/elimination in isolated guinea pig brain mitochondria under normal as well as respiration-impaired conditions. As measured by high-resolution Oxygraph the rate of resting oxygen consumption was increased, but the ADP-stimulated respiration was unaffected by MB with any of the substrates (glutamate malate, succinate, or α-glycerophosphate) used for supporting mitochondrial respiration. In mitochondria treated with inhibitors of complex I or complex III MB moderately but significantly increased the rate of ATP production, restored ΔΨm, and increased the rate of Ca(2+) uptake. The effects of MB are consistent with transferring electrons from upstream components of the electron transport chain to cytochrome c, which is energetically favorable when the flow of electrons in the respiratory chain is compromised. On the other hand, MB significantly increased the production of H2O2 measured by Amplex UltraRed fluorimetry under all conditions, in resting, ATP-synthesizing, and respiration-impaired mitochondria, with each substrate combination supporting respiration. Furthermore, it also decreased the elimination of H2O2. Generation of H2O2 without superoxide formation, observed in the presence of MB, is interpreted as a result of reduction of molecular oxygen to H2O2 by the reduced MB. The elevated generation and impaired elimination of H2O2 should be considered for the overall oxidative state of mitochondria treated with MB.

α-ketoglutarate dehydrogenase complex (KGDHc), or 2-oxoglutarate dehydrogenase complex (OGDHc) is a rate-limiting enzyme in the tricarboxylic acid cycle, that has been identified in neurodegenerative diseases such as in Alzheimer’s disease. The aim of the present study was to establish the role of the KGDHc and its subunits in the bioenergetics and reactive oxygen species (ROS) homeostasis of brain mitochondria. To study the bioenergetic profile of KGDHc, genetically modified mouse strains were used having a heterozygous knock out (KO) either in the dihydrolipoyl succinyltransferase (DLST^+/−) or in the dihydrolipoyl dehydrogenase (DLD^+/−) subunit. Mitochondrial oxygen consumption, hydrogen peroxide (H₂O₂) production, and expression of antioxidant enzymes were measured in isolated mouse brain mitochondria. Here, we demonstrate that the ADP-stimulated respiration of mitochondria was partially arrested in the transgenic animals when utilizing α-ketoglutarate (α-KG or 2-OG) as a fuel substrate. Succinate and α-glycerophosphate (α-GP), however, did not show this effect. The H₂O₂ production in mitochondria energized with α-KG was decreased after inhibiting the adenine nucleotide translocase and Complex I (CI) in the transgenic strains compared to the controls. Similarly, the reverse electron transfer (RET)-evoked H₂O₂ formation supported by succinate or α-GP were inhibited in mitochondria isolated from the transgenic animals. The decrease of RET-evoked ROS production by DLST^+/− or DLD^+/− KO-s puts the emphasis of the KGDHc in the pathomechanism of ischemia-reperfusion evoked oxidative stress. Supporting this notion, expression of the antioxidant enzyme glutathione peroxidase was also decreased in the KGDHc transgenic animals suggesting the attenuation of ROS-producing characteristics of KGDHc. These findings confirm the contribution of the KGDHc to the mitochondrial ROS production and in the pathomechanism of ischemia-reperfusion injury.